The invention relates to a fluid transfer system for an offshore moored floating unit.
Often a fluid connection has to be made between a sea bed structure and a floating unit using a fluid line assembly. This floating unit can move relative to the seabed structure. This movement will be more considerable, with respect to the water depth, if the environment in which the unit is present is relatively harsh. To prevent overloading it is known to realize the fluid connection between the unit and the seabed structure in such a way that a relative displacement of the unit and the seabed structure is possible. For example a fluid line is used which has a wave shape to permit a relative movement.
As a final safety measure, a fluid line assembly connecting the seabed structure and the floating unit can be disconnected from the floating unit if the weather conditions become very unfavourable. However, it is clear that such a disconnection has dramatic consequences on the efficiency of a production well and is therefore not always the preferred option.
In the PCT-application W0 87/05876 a fluid line assembly is disclosed comprising a lower catenary connecting a seabed structure to a subsurface buoy, and an upper catenary connecting said subsurface buoy to a floating unit. The lower catenary comprises a flexible fluid line which extends downwards from the subsurface buoy to the seabed and lies from the contact point with the seabed over a distance of this seabed to the seabed structure. To-and-fro movement of the subsurface buoy is accommodated by the flexible line and results in movement of this flexible line over the sea bottom. On the one hand this could damage the flexible line adjacent to the place of contact with the sea bottom by wear. On the other hand deviation of the subsurface buoy is restricted because otherwise damage will occur to the fluid line through overbending or overstretching. A maximum of 15.degree. movement relative to the vertical is generally accepted. The subsurface buoy is connected through e fluid line with a floating unit.
According to one aspect the invention aims to provide a fluid line assembly which permits larger relative movements between a floating unit and a fixed seabed structure.
According to another aspect of the invention it is aimed that the subsurface buoy can be realized with e buoyancy body having lower buoyancy properties, so both reducing its costs end the mass of the Clump weight placed on the seabed which keeps the buoyancy body in position using a line or tether.